An improved cathode for alkaline fuel cells

The use of nickel foam as an electrode substrate in alkaline fuel cells (AFCs) has been investigated for bipolar cells incorporating an electrically conducting gas diffusion layer (GDL). Improved performance, compared to a previous design, was obtained by adding an extra active layer (AL) composed of manganese (IV) oxide (MnO2) deposited onto carbon black. This new cathode design performed significantly better (130 mA cm−2 at 0.8 V and 25 °C) than the previous design (35 mA cm−2 under the same condition), especially at higher potential. It has been shown that the GDL is a key component of the gas diffusion electrode for both performance and durability, especially with liquid electrolytes. Electrochemical impedance spectroscopy was used to study the various losses in the cathode as a function of electrolyte concentration, oxygen concentration and cell voltage. The typical impedance spectra consisted of one high frequency depressed semi-circle which is believed to be related to porosity and KOH wettability, and one low frequency semi-circle related to electrode kinetics.